Laser fuses may be used to rewire semiconductor memory and logic circuits. For example, in dynamic or static memory chips, defective memory cells may be replaced by blowing fuses associated with the defective cells, and activating a spare row or column of cells. This circuit rewiring using fusible links allows considerable enhanced yields and reduces the production costs. Also, logic circuits may also be repaired or reconfigured by blowing fuses. For example, it is common to initially fabricate a generic logic chip having a large number of interconnected logic gates. Then, in a final processing step, the chip is customized to perform a desired logic function by disconnecting the unnecessary logic elements by blowing the fuses that connect them to the desired circuitry. Still other applications of laser-blown fuses are possible.
As shown in FIG. 1, a conventional laser fuse structure 10 typically includes one or more laser fuses 20. The fuse 20 conventionally includes a straight metal fuse line 21 extending through an inter-metal-dielectric (IMD), between block-like metal connector structures 22a and 22b. The block-like metal connector structures 22a and 22b enable the fuse line 21 of the fuse 20 to be electrically connected to one or more circuits disposed below the fuse 20. The one or more circuits connected to the fuse 20 may be modified or altered (e.g., reconfigured or repaired) by vaporizing a section 21a of the metal fuse line 21 (FIG. 2A) with a high energy laser to create an open 23 in the fuse line 21 as shown in FIG. 2B. The open 23 is defined by a trench 31 in the IMD 30 where the vaporized metal fuse line section 21a was disposed.
A major problem with the laser fuse 20 is that when the section 21a of the straight fuse line 21 is vaporized, the trench 31 in the IMD 30 left by the open 23 in the fuse line 21 provides a short and direct diffusion path 40 for metal atoms between opposing end portions 24a and 24b of the open fuse line 21 as shown in FIG. 2C. The short and direct diffusion path 40 allows the metal atoms of the opposing end portions 24a ad 24b of the open fuse line 21 to quickly migrate (reflow) toward one another during post-anneal reliability testing and evaluation. If the laser energy utilized in the fuse blowing process is not high enough, the fuse line end portions 24a and 24b may re-connect with one another causing the repaired device to fail again. If the laser energy utilized in fuse blowing process is sufficiently high to avoid metal atom reflow, the inter-metal-dielectric IMD 30 adjacent to the fuse line 21 may crack due to the extreme thermal expansion of the IMD 30 during the fuse opening process.
Accordingly, a laser fuse structure for repairing and reconfiguring integrated circuits is needed that substantially eliminates the metal reflow and IMD cracking problems of current laser fuse structures.